chore: standardize Nim builds to out/ subdir, simplify .gitignore

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SAC_LSTM_Bot_garage/make_twin.sh

@@ -17,7 +17,7 @@ set -euo pipefail
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
 TARGET="${1:-${SAMPLE_BOTS_DIR:-/home/davide/Projects/tank-royale/sample-bots/java/build/archive}}/SacTwin"
-BIN="$SCRIPT_DIR/SAC_LSTM_Bot"          # nimble build -d:release output
+BIN="$SCRIPT_DIR/out/SAC_LSTM_Bot"      # nimble build -d:release output (out/ subdir)
 SEED="$SCRIPT_DIR/weights/sac_best.zip" # frozen baseline
 
 [ -x "$BIN" ]   || { echo ">>> $BIN missing — run 'nimble build -d:release' first"; exit 1; }